Engine overheating/ A/C not running

BEATYGX

MEMBER
1994 BUICK CENTURY
6 CYL
FWD
AUTOMATIC

I have a 1994 Buick Century 3.1 with a problem overheating due to the fans not running. I have verified the fans do work as well as the fan relays. All wiring, relays, sensors, etc. Have been checked and are in good condition with no shorts. My AC compressor also does not energize. Again All wiring, relays, switches, etc have been checked.
I believe the problem is the PCM is not completing the Circuit to the Cooling fans relay coils or the A/C Compressor clutch relay coil. Also, I am not able to retrieve codes as two different code readers display they are not able to communicate with the PCM.
I have tried three different PCM's and still no results. The engine starts and runs very well otherwise.
Any Ideas would be appreciated, please.
Thanks!

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Okay, I would say it isn't a PCM. Regarding the fans, Have you checked or replaced the temp switch?

As far as the AC, is there power to the clutch? If you run a jumper wire to it, does it engage?

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Monday, January 14th, 2019 AT 9:41 AM

BEATYGX

MEMBER
2 POSTS

This car does not have a temp switch, just a temp sensor and I have replaced this. I can jump the ground side of the relay coils(this is the same side or wire which on the wiring diagram is labeled "Relay Control" at the PCM) and the relays engage and fans run.
As for the A/C, the only time the compressor clutch engages is when I jump the ground side of the relay coil (same side or wire on the wiring diagram labeled "Relay Control at the PCM.
I have also checked for voltage at all locations, Ground connections at all locations, and all wires involved for continuity and whether or not there are any shorts. I found everything to be good. It just appears for some reason, the PCM is not completing the circuits to engage the relays.

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Monday, January 14th, 2019 AT 9:41 AM